What energy is being transformed an electric blanket warms a bed on a chilly night

The answer is Endothermic!

Explanation:

Your body is taking in the heat.

Electric blankets have insulated wiring woven into them. When plugged in and turned on, the electric energy recieved from the electrical outlet is transferred to heat.

Electricity naturally produces heat when conducting, and by using insulation on the wires, this temperature can be controlled and gently warm the person whom the blanket is covering.